The JPMorgan board's governance committee, responsible for hiring new members, relies almost entirely on referrals from management to find director nominees, according to two sources familiar with the bank's practices and a review of bank regulatory filings. All of the other 10 largest U.S. banks say they use executive search firms, which have knowledge of a range of possible candidates.

An examination of the bank's selection process, which until now has been little known, could prompt questions about how much influence Dimon has over the largest U.S. bank's board.